The present invention relates to a system for detecting the state of a switch device having at least two states.
It is desirable to monitor the state of an actuatable switch device in various types of electrical devices. In an automobile, for example, numerous vehicle accessories are responsive to the operative position of a vehicle ignition switch. Typically, a direct connection from the vehicle ignition switch to a monitoring circuit is used to detect whether the vehicle ignition is ON. This conventional approach is illustrated, for example, in U.S. Pat. No. 2,698,893, U.S. Pat. No. 4,926,025, and U.S. Pat. No. 5,229,579. Similarly, U.S. Pat. No. 4,903,011 discloses a lamp drive circuit having a main drive circuit and a separate back-up drive circuit for energizing a lamp through a vehicle ignition switch.
The present invention is directed to a system for detecting the state of a switch device having at least two states. The system includes a driver circuit having an output operative to provide a driver output signal. An indicator is electrically connected between the driver circuit and the switch device. The indicator is activated in response to the driver output signal and upon the switch device being in a first state. The system also includes a monitoring circuit electrically connected to a node between the indicator and the driver circuit. The monitoring circuit is responsive to the switch device through the indicator. The monitoring circuit is operative to provide a signal in response to the switch device being in the first state and a second signal in response to the switch device not being in the first state. Preferably, the signal from the monitoring circuit is operative to effect energization of a controller which controls operation of associated electrical equipment, including the driver circuit.